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Hmm why do paintball hits leave RING welts??

Everytime ive been shot (minus face mask hits) that leave welts they make a ring mark, is it when the paintball flys the fill goes to the back, so there is no paint in the tip and when it hits, the outeredge hits first then the center, but buy then its broke so that part doesnt marks. Thats my theory, is there any proof of this by comp evidence?? im confused

The answer is easy enough, lets see if I can explain it...
OK, from geometry we know a triangle is the strongest shape, and a circle, or sphere in this case, is the weakest. As the paintball hits you the front of the shell crumples, having no support. The edges around the 90* axis, however, have a lot of support from the shell around it. Thus these edges drive forward for a lot longer than the front part of the shell without crushing. And we are left with those ringworm looking marks and cuts we love so much.
V

hmmm....

I don't think the triangle the strongest shape. I guess it would all depend on the context of where it was used. Think of a dam, a dome or even the aquaducts those silly romans built. All of those structures use an arch to distribute the loads to the outer edges of the shape

Also... if you look closely at your mask, under the correct lighting, you will see lots of rings from where the paintballs have hit.

A good way to visualize the mechanics behind this effect is to take a standard sheet of paper and roll it up into a tube about 1 inch in diameter. If you pinch the tube to collapse the diameter you'll notice very little resistance. Now, if you stand the tube on end and gently push on the top, hand covering the open end of the tube, you'll notice much more resistance to your pushing. This is *basically* the same effect that causes the ring welts... of course the impact loads peak only for an instant when the ball has collapsed enough to bring it's maximum diameter into contact with your skin.

Redkey,
I guess I should explain. Arches and domes are great designs to work with if you have an equal amount of pressure distributed throughout the arch. They have a tendency to "fall into themselves", making them a very stable platform. This is also evident in deep-sea engineering, the constant high pressure of the ocean distributed evenly across a sphere or dome makes it very practical.
But this doesn’t change the fact that triangles are still stronger (Don’t believe those Volkswagen commercials!). In terms of simply bearing a load, or withstanding an impact, the equilateral triangle is the strongest shape. The load of a triangle is going to be distributed to only three points, rather than the infinity points of a circle. This is evident if you have any kind of CAD program that does load testing; a triangle can withstand as much as 15% more weight than an arch can (assuming that you are using the same width). For example, a bridge might be arched, but if you look at it's support structure, it will probably have crossbeams in the shape of a triangle.
By the way, your example with the paper cylinder was excellent. I was trying to think of a way to explain what I was thinking, but you nailed it perfectly.
V

Since we were talking spheres I figured the arch was perhaps a more suitable geometric shape. I didn't spend much time really thinking about this... i suppose I could have pulled out the statics book to add a little more meat to my statement. Instead I used the quick and cheesy way to defend my statement by saying.... "I guess it would all depend on the context of where it was used"

True, the triangle is probably the most commonly used structural element. We see it time and time again when we constrain our FEA software to certain hardpoints and tell it to fill the enevelope with a part that will handle the predicted loads. The software will optimize the size and shape of the part, modelling all types of shapes and geometries before producing a model of a part that most efficiently meets our requirments. Many of the parts come out looking very organic... It's pretty nifty stuff.

if u really think about it they said that the triangle is the strongest and the circle is the weakest. the triangle has the least amount of sides a polygon can have and in science my teacher explained to us that a circle is jus millions and millions of sections of straight lines. if u take a circle the diameter of the sun and look at it from a foot away the line would seem to be straight

BLOOD!!!!

The dome shape of the paint ball forces the blood in the impact area from the center of ground zero to the outside edges of the paintball dia. causing the capillaries on the outside dia. to hemorrage(bleed/leak/break)leaving the inner portion of the impact area strangely pale for awhile, due to the blood that was forced out. Hence a RING is born! Then whole area of impact may or may not bruise depending on how much capillary damage was done and where the hit occured. Either giving you a RING bruise or a BIG *SS one. Im sure angle of impact figures in, relating to the shearing forces on the skin and capillaries. You will normally get more bruising over soft tissue areas than over bones where the shell of the ball is more likely to break the skin. Example: The knuckles of the hand. Ouch! But hardly a bruise. But of course this how I look at things because I am a R.N.
BTW I believe its the velocity of the paint in the ball that causes the ball to break not the impact of the shell, otherwise it would bounce off of you like a ping pong ball or a super ball. So, to those people want to freeze their paint to hurt someone, sure it will hurt but you will never tag any one out.

The strongest shape with equal mass is the the cylinder and neither of the above.

This is due to the physics that was mentioned above.

1.) a triangle (we will use cone because of the 3d aspects are equal) will generate force on an edge (the base or the tip which ever is the weakest)that is fixed to a point but dispersed over a larger area than say a rectangle of equal mass.

2) A sphere is incredibly strong as it can displace load over its conplete area (that is if the area is placed over the complete area) a paintball hit is generating all of the force at a minute point of impact, therefore crushing the leading edge of the ball.. Remember there is equal force around the back side of the ball in flight minus turbulance.

3.) when the leading edge of the ball collapses you get a doughnut pattern because the trailing edge is the last to compress before rupture stress is generated. This then creates a very strong pattern that would most ressemble a thick cylinder (which has the GREATEST vertical ridgity). at breaking point, the mass of the paint is expelled outward into this "doughnut" (I think the correct name for this shape is a toride, but I am not sure and I am not in the mood to surf for it... so look it up if you want )

This is the reason for the circular bruises. The force is in a circular pattern.

This is what VALCONE said, but with more correct geometry and physics added into the mix...

First, remember that not all materials break apart in the same manner. I do not believe that Perfect Circle Paintballs leave a circular welt.

Second, when determining what shape is the strongest you have to consider what forces it will be resisting. A cylinder is not the strongest when the force is applied to an small point on it's "side". The same is generally true with most shapes that have a side. It all depends on where/what type of force is being applied. That's why we see different shapes being used in different applications.

more drivel

Shades... interesting. I never thought of it from a "hydrostatic shock to the body" standpoint. It's probably some combination of the two events.

Lamby...

1. Not sure I follow this, could you please elaborate?

2. What do you mean by equal force on the back side of the ball during flight? If the forces on the front and the back of the ball are equal then the ball isn't moving. Perhaps I just missed something.

3. Leading edge compressing to create a toroid? Trailing edge last to compress before rupture stress? Do you have time to sketch this out? I've having a hard time visualizing the effect(s) you are describing.

Re: more drivel

[QUOTE]Originally posted by Redkey
[B]
Lamby...

2. What do you mean by equal force on the back side of the ball during flight? If the forces on the front and the back of the ball are equal then the ball isn't moving. Perhaps I just missed something.

All right, let me see if I can make this a little easier to follow... The paintball will have two phases of travel in its flight: acceleration, and deceleration.

1. Acceleration is the the act of making the ball overcome the enertial forces that are keeping it still.. IE friction of the breech and gravity. (this is done by firing the marker)

2. Deceleration is every point after the maximum acceration velocity is achieved. Once the paintball has reached maximum velocity, only two factors will slow it down. 1) aerodynamics (in the air) and 2) friction (air, object, skin, ect).

Now this is where it gets more confusing, since only those factors are going to effect the distance the ball will travel before it will slow down. you will have to look at the physical makeup of the ball as opposed to the resistance (friction) that is enacted upon it. (where does it hit? a sup-air bunker will prob deflect the ball, where as a brick wall will not.)The reason the paintball disforms is due to the fact that it was designed to "give" before skin will.

So, you take a paintball that is past its acceration phase.. there is now an even pressure behind the ball.. ( which is slightly below atmospheric pressure - minus turbulance) and a resistance to the front of the ball caused by the movement of air across the surface of the paintball.

When this paintball hits an object like your skin. The first part of the ball to contact you will have a MUCH greater force of resistance (friction) than the rest of the sphere has acting upon it. This is not the point that is suffering the greatest amount of stress. But since the paintball is not a true solid there is give designed into the shell and its contents. The shell at the leading edge will start to compress. this forces the paint inside to move out of the space that it was currently occupying. It will move back and to the sides (there is no where else for it to go).

As the ball continues forward tring to push itself into the resistive object (your skin). Structial integrety of the object is being comprimised. The paint that was pushed to the outside and back of the sphere still needs to travel somewhere as the ball continues to compress. now the back of the ball will start to colapse (just like the front) because the structure is stronger on the outside of a half circle than the middle.

This will push more paint into the outside of the shell. There is some point when the shell can no longer withstain the pressures that are building up inside of it colapsing self and ruptures. This will then allow the trailing edge of the pall to continue its compression because now there is very little resistance to over come until it compresses into the leading edge.

What you will have at one point is a ball that has a good majority of its mass of the outside of the sphere. the point with the then greatest structual strength. Thus why even if you gog someone you still get the circular rings (look at your goggles you might see some of the same rings you get as welts)

3. Leading edge compressing to create a toroid? Trailing edge last to compress before rupture stress? Do you have time to sketch this out? I've having a hard time visualizing the effect(s) you are describing.

I will do a photoshop version if I have time (which I dont today.) the best even though greatly exagerated view would be a picture of a red blood cell.

The arch is a strong structure but not the strongest. The arch spreads the downward force out across the whole arch ultimately depending on the bases to be held in place. As long as the base of the arch is secure, the arch will be sturdy. However, you have to depend on something to hold the base, so it isn't strong on its own.

A sphere on the other hand is very weak. When pressure is applied to any part of it, the sphere will give, and lose shape/collapse. If you push down on the top of a sphere, the top half or upper hemisphere distributes the force outward from the center of the sphere. However, the bottom half of the hemisphere does NOT keep the walls of the sphere from collapsing outwards. Instead, the shape pancakes. It's pretty much the weakest 3 dimensional object.

The strongest structure is a four sided object made of equilateral triangles(3 sided pyramid). The triangular design won't shift like a box. (ignore the dots in the following shapes as this board doesn't recognize blank spaces. Without the dots/periods the characters used to make the objects would just be bunched together forward and backward slashes)
..______
./......../
/_____/

The weakest areas on a triagular object are obviously the midpoint of any side. By simply putting another triangle inside of that triangle you strengthen that point.
...../.\
..../...\
.../___\
../.\..../\
./...\../..\
/___\/___\

With repeating the triangle inside of triangle inside of triangle design infinately, you theoretically have an uncollapseable object because every time there is a weak point(midpoint) a new triangle is there to re-enforce it.

As far as the ring for a bruise, my theory is that when the edge of the paintball first hits you, the paint inside the sphere is driven outward towards the walls of the paintball(see above about the sphere). Once it is against the wall of the paintball it has nowhere else to move. That means that a large part of the mass is against the wall of the ball in a ring shape as it slams into you. The brunt of the force is a ring of paint. Granted it, this is just my "theory", or rather hypothesis as I have not tested this in any way.

Re: BLOOD!!!!

Originally posted by shades The dome shape of the paint ball forces the blood in the impact area from the center of ground zero to the outside edges of the paintball dia. causing the capillaries on the outside dia. to hemorrage(bleed/leak/break)leaving the inner portion of the impact area strangely pale for awhile, due to the blood that was forced out. Hence a RING is born! Then whole area of impact may or may not bruise depending on how much capillary damage was done and where the hit occured. Either giving you a RING bruise or a BIG *SS one. Im sure angle of impact figures in, relating to the shearing forces on the skin and capillaries. You will normally get more bruising over soft tissue areas than over bones where the shell of the ball is more likely to break the skin. Example: The knuckles of the hand. Ouch! But hardly a bruise. But of course this how I look at things because I am a R.N.
BTW I believe its the velocity of the paint in the ball that causes the ball to break not the impact of the shell, otherwise it would bounce off of you like a ping pong ball or a super ball. So, to those people want to freeze their paint to hurt someone, sure it will hurt but you will never tag any one out.

I agree with the part that the impact forces the blood out to the edges. excellent